Pump comprising a balance arrangement and a related method

Abstract

A pump ( 110 ) is disclosed comprising: an inlet ( 114 ) being in fluid communication with an inlet cavity ( 115 ); an outlet ( 118 ) being in fluid communication with an outlet cavity ( 119 ); a motor ( 120 ) being arranged in a motor cavity ( 121 ); a pump axis ( 122 ) being rotatably drivable by the motor: impellers ( 124 ) being positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and a balance arrangement ( 126 ) configured to at least partially offset an axial thrust affected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising: a balance cavity ( 132 ); a balance drum ( 128 ) arranged between the outlet cavity and the balance cavity; and a balance line ( 134 ) extending between and fluidly connecting the balance cavity and the inlet cavity. The inlet is in fluid communication with the inlet cavity via the balance cavity and the balance line. A related method is also disclosed.

The invention claimed is: 
     
       1. A pump comprising:
 an inlet in fluid communication with an inlet cavity; 
 an outlet in fluid communication with an outlet cavity; 
 a motor arranged in a motor cavity; 
 a pump axis rotatably drivable by the motor; 
 a number of impellers positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and 
 a balance arrangement configured to at least partially offset an axial thrust effected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising:
 a balance cavity; 
 a balance drum arranged between the outlet cavity and the balance cavity; and 
 a balance line extending between and fluidly connecting the balance cavity and the inlet cavity; 
 wherein the inlet is in fluid communication with the inlet cavity via the balance cavity and the balance line. 
 
 
     
     
       2. The pump according to  claim 1 , wherein the motor cavity is separated from the balance cavity by a rotary seal through which the axis runs. 
     
     
       3. The pump according to  claim 2 , wherein the rotary seal is configured to allow leakage of a barrier fluid from the motor cavity to the balance cavity. 
     
     
       4. The pump according to  claim 1 , wherein the balance arrangement is configured to allow leakage of a balance fluid from the outlet cavity to the balance cavity. 
     
     
       5. A method of pumping an inlet fluid using a subsea pump, the subsea pump comprising:
 an inlet in fluid communication with an inlet cavity; 
 an outlet in fluid communication with an outlet cavity; 
 a motor arranged in a motor cavity; 
 a pump axis rotatably driven by the motor; 
 a number of impellers positioned between the inlet cavity and the outlet cavity and being actuatable by the pump axis to cause a differential pressure across the inlet cavity and the outlet cavity; and 
 a balance arrangement configured to at least partially offset an axial thrust effected upon the axis by the impellers when the pump is in operation, the balance arrangement comprising:
 a balance cavity; 
 a balance drum arranged between the outlet cavity and the balance cavity; and 
 a balance line extending between and fluidly connecting the balance cavity and the inlet cavity; 
 
 wherein the method comprises directing the inlet fluid to the inlet cavity via the balance cavity and the balance line. 
 
     
     
       6. The method according to  claim 5 , further comprising:
 separating the motor cavity from the balance cavity using a rotary seal through which the axis extends; 
 leaking a balance fluid through the balance arrangement from the outlet cavity to the balance cavity; and 
 leaking a barrier fluid through the rotary seal from the motor cavity to the balance cavity; 
 wherein the inlet fluid, the balance fluid and the barrier fluid are mixed in the balance cavity prior to being directed to the inlet cavity via the balance line.